The functionality of an image-related device is greatly enhanced when it is able to consistently provide the user with neat and usable output. The image-medium receiving tray of a device plays a crucial role in providing such enhancement.
An effective tray must be able to collect media of different sizes and types and do so in a manner that does not disturb, e.g. smear, the image. To be even more effective a tray should evenly stack the medium it collects.
To be all of the above, a tray must be designed with consideration given to the operating parameters of the associated image-related device. For example, the type of device determines the type and size of medium that the tray must handle--thereby affecting the size of the tray.
The device also defines the speed and angle at which the tray receives the medium--thereby also affecting the size, the angle at which the tray interfaces with the device, and possibly the shape of the tray. Current techniques of tray design are discussed below within the context of several design considerations.
(a) Size of image medium--Most devices process image medium of different sizes; accordingly the tray must be able to accommodate the same variety of sizes. To fulfill this requirement many devices simply use a large tray to handle the largest possible medium that the device can output.
It is desirable, however, that the device and tray be both compact and economical. These characteristics are preferably obtained by reducing the overall size of the tray and accommodating larger medium in other ways.
When the leading-edge portion of a sheet of medium curls downward relative to the trailing-edge portion of the medium--a phenomenon familiarly known as "flopping"--the system may lose control of the medium. In particular with a short tray, large medium flops over the front end of the tray (i.e., the end farthest from other components of the image-related device) and may completely slide over and off the front end of the tray.
One mechanism for accommodating large medium and preventing flopping is a multipiece tray. A multipiece tray includes a main tray and an extension tray--mechanically attached to the main tray and usually stowed beneath or within the main tray. The extension tray is extended to create, in combination with the main tray, a tray large enough to collect large medium.
Though adequate to accommodate large medium and prevent flopping, a multipiece tray is undesirable for several reasons. First, repeated extension and retraction of the extension tray and the stress it places on the mechanism joining the trays results in a device which is susceptible to breakage. Second, multipiece trays are a significant inconvenience to the user, who must repeatedly extend and retract the extension tray to accommodate various media.
Third, an extension tray and the associated mechanical attachments increase the amount of material required to produce the tray and thereby increase overall cost. Finally, when extended the extension tray creates a discontinuous and rough surface over which sheets of medium must slide. This discontinuity often causes sheets to slide erratically, resulting in an uneven stack of medium.
A second technique to accommodate larger medium is to transversely curl the medium along its entire length. This is usually implemented through use of a cylindrical-surface tray. Such a tray forces the medium to transversely curl--thereby giving rigidity to the medium. With this rigidity the medium can extend over the front end of the tray without flopping. A beneficial feature of this technique is that it operates relatively independently of the size of the tray. Though somewhat appealing, this technique is undesirable under certain operating conditions as explained below.
(b) Type of image processing--Another operating parameter to be considered when designing a tray is the type of image processing the device performs. An effective tray must collect and stack image medium in a manner that does not disturb the image just processed by the device. For example, in a liquid-ink device a sheet having wet ink is likely to smear when a subsequent sheet contacts it. One method of avoiding image disturbance in such a context is taught in U.S. Pat. No. 5,299,875 of Hock et al.
In Hock et al. a set of wing deflectors positioned near the exit slot of a portable inkjet printer imparts a W-shaped bow on the leading-edge portion of an emerging sheet. This bow imparts rigidity to the leading-edge portion--which allows it to extend over and above the output platform of the printer and the trailing edge of any already-dropped sheet or sheets at rest on the platform.
As the sheet continues to emerge, however, and the leading-edge portion of the sheet moves farther from the deflectors it begins to lose rigidity. When the trailing edge of the sheet exits the printer, the leading-edge portion completely loses rigidity and flops onto the already-dropped sheet--making initial contact toward the leading edge of the sheet. The trailing-edge portion, still bowed by the deflectors, remains at rest on top of the deflectors--separate from the already-dropped sheet.
When a subsequent emerging sheet contacts the bowed trailing edge of the previously exited (but not yet completely dropped) sheet it pushes the trailing edge forward past the deflectors. The trailing-edge portion loses its rigidity and falls onto the trailing-edge portion of the already-dropped sheet.
In limiting the initial contact between the sheets to their leading-edge portions, this device reduces the possibility of smearing since the leading-edge portion of the already-dropped sheet is driest. Also, in keeping the trailing-edge portions of printed sheets separate until a subsequent sheet begins to emerge, this device allows more time for the trailing-edge portion of the already-dropped sheet to dry before another sheet lands on top of it.
While generally effective in preventing smearing this technique is somewhat undesirable because it curls the medium immediately upon exiting the device--thereby curling the medium while the ink is wettest. Because the medium is curled while the ink is drying, the medium is likely to have a residual curl.
In addition, while Hock et al. teach a relevant principle, their implementation of the principle is in a portable ink-jet printer which does not use a tray to collect its output; it merely drops its output onto a table. Such operation is outside the field of the present invention as defined above, and undesirable in a printer intended for essentially fixed installation--as table space is assumed to be at a premium, and a printer is commonly positioned with its tray extending over the table edge (except when not in use and stowed within the printer).
(c) Stacking of image medium--A common problem associated with trays is uneven stacking of sheets of image medium. This problem occurs when sheets ejected from a device slide in a disorderly fashion on the tray surface and particularly on previously deposited sheets.
The result is a pile of misaligned or sometimes even scattered sheets. The user has no option but to manually even the edges of the medium.
A factor contributing to uneven stacking is the manner in which the tray receives the medium from the device. Some typical devices have their trays positioned so that the leading edge of each sheet of medium slides from the back of the tray (i.e., the end closest to other components of the image-related device) toward the front. While sliding, the medium encounters resistance and discontinuities in the tray surface or resistance from previously deposited medium. This resistance sometimes causes the medium to move erratically.
A common technique to achieve even stacking is to add stops at the front end or along the sides of the tray, or both. As with the multipiece tray design previously mentioned, such mechanical additions to the tray are inconvenient, costly, and susceptible to breakage.
Another mechanism for even stacking in inkjet devices uses a pair of longitudinally extending wings driven by an electromechanical assembly. The wings initially hold a newly printed sheet spaced above a previously printed sheet. After printing is complete, the wings move apart, allowing the printed sheet to drop onto the previously printed sheet.
Therefore the sheets fall into an orderly stack. Though quite effective in stacking medium, this mechanism may be relatively more costly.
(d) Summary of related techniques--As previously stated, common techniques for designing effective trays generally include the use of a simple planar surface with various mechanical additions such as extensions and stops. More sophisticated designs have used cylindrical surfaces to control the shape of the medium or electromechanical wings to control the placement of medium.
These techniques, while providing trays that enhance device functionality, create problems in other areas. For example, transverse curling of wet medium--either by deflectors or by a cylindrical surface--causes the medium to have a residual curve. The use of a multipiece tray creates surface discontinuities which may cause uneven stacking of medium. A final problem is that the trays produced by some of these techniques--with their extensions and stops or electromechanical wings--are economically inefficient.
(e) Previously unrelated techniques--In a field not previously associated with the interaction between trays and solid but very flexible image media, it is known to use B-spline curves to design surfaces. Such surface design is common in the automotive and aerospace industries, where the interaction between surfaces and fluids is closely scrutinized to optimize machine performance and efficiency. Such techniques are also common in the field of industrial design, where they are used in shaping common household products to help find aesthetically pleasing forms.
As previously stated, the B-spline surface design technique has not been previously associated with, or suggested for use in, the functional design of image-medium receiving trays.
(f) Conclusion--Thus important aspects of the technology used in the field of the invention remain amenable to useful refinement.